Air conditioning, radiant surface and displacement ventilation systems are used in enclosed spaces such as buildings, vehicles and equipment trailers, to provide cooling for equipment and thermal comfort for people. This is achieved by providing an adequate flow of air to the enclosed space with the air supply, when necessary, having been cooled and dehumidified; a typical state for the supplied air could be 13° C. and 65% relative humidity. In conventional systems, the thermal load of the space is dissipated entirely by using sensible heat transfer into the air stream and this determines the required air flow rate for the space; a typical state for the air leaving the space could be 24° C. and 35% relative humidity.
The low value of the relative humidity in the exhaust air represents an unused cooling potential that can be used, via latent heat transfer, to substantially increase the capacity of the air stream to remove thermal energy from the space. This potential cannot be realised by direct evaporation into the space because the increased humidity would reduce the comfort condition for occupants and any wet surfaces could represent a hazard with electrical equipment.